The present invention relates to a color discrimination vision test and more particularly to an apparatus and method which can be used to identify color vision deficiency and the degree of deficiency, if any, a test subject has.
Color discrimination testing is essential for many types of jobs where the ability of a person to recognize different colors is a fundamental part of a job. Color discrimination testing may also be used for diagnostic purposes to recognize medical conditions that may require attention. Prior art patents, including for instance U.S. Pat. No. 4,848,898 to Massof, describe in detail the human visual system and basic color deficiencies that may be discovered.
Several different tests are widely recognized and practiced. These tests include Ishihara plates, the Munsell-Farnsworth test, and Nagel's anomaloscope.
Ishihara's plates require the detection of numbers which are displayed in front of a background. The numbers and background are built up by spots varying in diameter and in hue. The hue of the spots is selected such as to cause confusion in color perception in color deficient people. Therefore, color deficient people are not able to group those spots together to form the number which is to be detected. Ishihara plates are used to detect red-green color deficiency. A short version of the test is used to determine color vision performance in a passed/failed manner for red or green color vision. The full test can additionally discriminate between "strong" and "weak" deficiency in color vision (two levels). Ishihara's test is very popular in clinical use as well as in the laboratory. Since the colors on the plate are produced by reflection of ambient light, the ambient light must have a specific spectrum (daylight) and must be of a give luminance (&gt;500 lux) to ensure correct test conditions.
In the Farnsworth-Munsell test, 15, 65 or 100 filled circles (depending on the test) of varying hue are placed in random order on a table. The patient is asked to order the circles in a row so that neighboring circles differ as least as possible in color. The first color (hue=blue) in this row is fixed and given by the test. The Farnsworth-Munsell color test requires similar conditions for illumination as mentioned above for the Ishihara test. The interpretation of the results is somewhat more complicated than is the case for the Ishihara test. However, Farnsworth-Munsell enables an administrator to check for red-green as well as for blue yellow deficiency. Detection of degree of deficiency depends on one hand on the number of color circles used. An increasing number of circles goes in parallel with an increasing time needed to complete the test. For this reason, most administrators prefer to use the Farnsworth-Munsell version with 15 circles. On the other hand, the degree of deficiency can also be assessed (two levels) by using a desaturated version of the Farnsworth-Munsell test. However, this procedure sometimes makes the interpretation of results somewhat complicated (e.g. in the case where patients perform better in the desaturated test than in the standard test).
In the so called anomaloscopes (e.g. the Nagel anomaloscope), patients match the hue of two fields. One of the fields has a given hue. The complete anomaloscope test should be performed for different levels of luminance of the field with a fixed hue. The matching procedure consists in varying the luminance of two colors (in case of the red-green test, red and green) which are mixed and comparing the hue of the mixture to the hue of the field with a fixed hue.
Ishihara's test requires the test subjects to communicate the number detected. If the numbers are communicated verbally, the presence of a person is required to record the response. Recording of the information without a test administrator would require test subjects, e.g., to key in the number on a keyboard or a key pad. They therefore would have to change their fixation from the test plates to the keyboard. Beside ergonomical problems, the change of fixation will alter the state of a patient's visual system (e.g. change in level of adaptation) affecting therefore, the result of the test. Similar conditions are also true for the Farnsworth-Munsell and anomaloscope tests mentioned above.